Edging the ski means to angle the ski base away from the snow so the load concentrates more on the edge of the ski. Edging the skis is an absolute necessity in order to turn, stop and to stand still on an inclined slope.
You can actively edge your skis through:
Edging with your knees, which is basically an inward rotation of the femur. Out of your ski boots it is also possible to angle the ankle, but with the boots on this movement is very limited. However, there's still some edging to achieve through moving the foot.
Edging with your hip. With increasing speed, it's near impossible to sustain the increasing forces through edging only with the knees. It's then necessary to involve the hips. To edge with your hip you simply angle the hip inwards and the skis will get on edge.
Edging with the body. When you're going really fast it becomes necessary to edge the skis by leaning your entire body into the turn.
Edging entails an ever-changing movement. In low speed the knees initiate the edging in the turn. As you gradually move through the turn the knee edging gets supported from using the hip angle and body lean. Without speed and momentum, though, it's impossible to lean since you'd then fall over.